1. Field of the Invention
This disclosure relates generally to heat and fire resistant plastic foam that can be used in building construction and, more particularly, to a heat and fire resistant plastic foam having at least one layer of an intumescent coating comprising expandable graphite for protecting the plastic foam from heat and fire.
2. Background
The effectiveness of plastic foam as a thermal insulation material makes it suitable for an extensive range of insulation applications including residential housing, commercial offices, warehouses, industrial, institutional, and retail buildings, and in refrigeration, aerospace and marine applications. Plastic foam can be used in many construction applications, including flat and pitched roofs, wall cavities, floors, internal linings, composite decks, aircraft cavities, hulls, tunnels, mineshaft ducts, pipes, and storage tanks
A drawback of plastic foam is its high flammability. Building codes generally have two requirements for plastic foam. First, the plastic foam should have a flame spread index of less than or equal to 75 and a smoke-developed index of less than or equal to 450 when tested in accordance with ASTM E-84, “Standard Test Method for Surface Burning Characteristics of Building Materials.” Second, the plastic foam should have an approved thermal barrier on the habitable side of a structure between the interior of the structure and the plastic foam. Thermal barriers are required for interior surfaces to reduce the risk of a flash fire and to extend the time at which the plastic foam would reach its auto-ignition temperature should a fire originate from other sources.
A common thermal barrier is ⅝ inch gypsum wallboard or drywall placed over the plastic foam. Alternatively, prefabricated sandwich panels of gypsum wallboards or gypsum fiber boards with insulating panels made from plastic foam are used. A drawback for either approach is that the addition of a gypsum wallboard or the construction of a sandwich panel significantly increases the materials cost and associated labor for installation of the gypsum wallboards or sandwich panels.
An alternative to the use of wallboard to provide a thermal barrier is to apply cementitious or cellulosic coatings. To be effective thermal barriers, these materials must generally be sprayed on at thicknesses of greater than or equal to about 50 mil (0.05 in.), requiring several coats. These coatings are not aesthetically pleasing for many exposed indoor environments. The friable nature of these coatings makes them unsuitable for application in an area that receives direct contact, vibrations, or foot traffic.
In general, building codes accommodate an alternative to the requirement for a thermal barrier providing the plastic foam passes a large-scale fire test. Examples of large-scale fire tests are NFPA 286, “Standard Methods of Fire Tests for Evaluating Contribution of Wall and Ceiling Interior Finish to Room Fire Growth”; UL-1715, “Room Fire Test Standard for Interior Finish Materials”; UBC 26-3, “Room Fire Test Standard for Interior of Foam Plastic Systems”; and FM 4880, “Approval Standard for Class 1 Insulated Wall or Wall and Roof/Ceiling Panels, Plastic Interior Finish Materials, Plastic Exterior Building Panels, Wall/Ceiling Coating Systems and Interior or Exterior Finish Systems.” These large-scale fire tests are sometimes referred to as “room corner tests” because the ignition source is placed in the corner of a full-scale test room with walls and ceiling made from the system to be tested.
Therefore, an intumescent coating that will enable plastic foam to pass large-scale room corner fire tests is needed. It is highly desirable that the intumescent coating composition can be applied simply and economically with minimal labor costs. It is also desirable that the intumescent coating composition is non-toxic, has low VOC's, is non-friable, and is aesthetically pleasing.